1. Field of the Invention
The present invention relates to a powder coating material feeding apparatus and, more particularly, to an apparatus which transfers a powder coating material received in a metal drum from a coating material manufacturer to a powder tank for a powder coating system.
2. Description of the Related Art
Powder coating has drawn attention as an environmentally friendly, pollution-free coating method because it uses no solution. In powder coating, a powder coating material that is sucked through a conveying hose from the powder tank is fed to a powder coating gun, which sprays the powder coating material onto the surface of an object to be coated, and the coating material is thus deposited on the surface of the object.
To continuously perform such a powder coating, the powder coating material has to be continuously or intermittently fed to the powder tank to keep it filled. The powder coating material is typically supplied in a 200-liter metal drum from a manufacture of coating material. Japanese Patent Laid-Open No. 59-74818 discloses a powder transfer apparatus that directly feeds a powder coating material from a metal drum to a powder tank. In this powder transfer apparatus, a nozzle is introduced into the metal drum supported in its fully upright position or tilted position, and an ejector pump connected to the top of the nozzle sucks up the powder coating material. The ejector pump lets compressed air to pass through the top portion of the nozzle to form negative pressure therewithin. With utilizing this negative pressure, the powder coating material is drawn from the tip of the nozzle to the top portion thereof to be fed with the compressed air.
The use of the ejector pump to suck up the powder coating material from within the drum requires a great deal of compressed air. Since the compressed air and the powder coating material are mixed, a cyclone is conventionally used to separate the powder coating material from the compressed air and to feed it to the coating gun. Part of the powder coating material drawn from the drum is thrown away along with the compressed air without being collected at the cyclone, resulting in the deterioration of the utilization efficiency of the coating material.
In the above method in which the ejector pump sucks up the powder coating material by utilizing negative pressure, a feeding rate capacity is 2 kg/min. or so at the highest. In a coating operation requiring a great deal of coating material, such a level of feeding rate is insufficient.
When changing the coating color, the conveying path of the powder coating material has to be cleaned by an air purging or the like, and the cleaning of the nozzle, ejector pump and cyclone is time-consuming.
The use of a great deal of compressed air to transfer the powder coating material possibly causes an impact fusion in which the powder coating material adheres to the inside of the conveying path. The conveying path may be clogged, and an old coating material once adhered to the conveying path is newly transferred and reaches the surface to be coated, thereby degrading coating quality.